While KSA would be the biggest news, Qatar would be the biggest indication of a major shift, and would send a message to Iran that they are being isolated while Israel is being embraced. Of course China and Russia will be influencing Qatar in ways that we may never see. If Trump can overcome that (and get reelected), there will be a major shift in power in the Arab world.
I’ve got six good guesses posted (one was a gimme from the President’s own lips Saudi Arabia) - so we still need at least 1-3 more (assuming all mine are right).
Tunisia? Algeria?
Yemen?
Imagine Iraq - that would be a sharp stick in the eye of the Iranian regime - the Kurds would vote for it, and the Sunni tribes are close to the Saudis. The new PM is more independent from Iran.